Since new compounds of medical interest continue to be isolated from natural sources, the elucidation of the structures of natural products remains an inportant and challenging problem. The application of mass spectrometry to structure determination has had some success; unfortunately, however, only a few peaks in a typical natural product's mass spectrum have real diagnostic significance. This is due primarily to the fact that, in a complex mass spectrum, a given peak may be formed from several distinct precursors, making structural conclusions hazardous. It is proposed that the recently developed "metastable defocussing technique" will permit unambiguous determination of the precursors of a given peak, and thus allow conclusions about the structure of the parent compound. Initial studies on the feasibility of this approach will be conducted on steroidal compounds.